Conventionally, a rotating electrical machine (hereafter referred to appropriately as a motor) has been known as an electric motor for converting electrical energy into mechanical force, or an electrical generator for carrying out the opposite conversion. A motor generally comprises a substantially cylindrical stator having coils respectively wound around a plurality of teeth sections that are formed projecting inwards, and a rotor provided capable of rotation inside the stator.
As the rotor, the structure shown in FIG. 7, for example, is known. This rotor 50 comprises a rotor core 52 forming a cylindrical shape, a rotor shaft 54 passing through a center part of the rotor core 52, end plates 56 arranged in contact with both sides of the rotor core 52 with respect to an axial direction of the rotor shaft 54 (and rotor core 52) shown by the arrow X, and a fixing member 58 for fixing the rotor core 54 and the end plates 56 on the rotor shaft 56.
The rotor core 52 is formed by integrally coupling a large number of magnetic steel plates, that have been respectively formed by punching silicon steel plate etc. into a circular shape, by laminating in an axial direction and fastening. Also, a plurality of magnets are formed inside the rotor core 52, close to the outer periphery, by embedding a plurality of permanent magnets 60 at equal locations in the circumferential direction.
The rotor shaft 54 is formed from a round steel bar, with a flange section 55 protruding outward in a radial direction formed on an outer periphery. This flange section is brought into contact with an end plate 56 when the rotor 50 is assembled and functions as a contact section for setting an axial position of the rotor core 52 on the rotor shaft.
The end plate 60 is constructed using a circular plate having substantially the same outer shape as an axial direction end section of the rotor core 52. It is common practice, in the end plate 60, to use as a metal an aluminium plate that is comparatively lightweight, inexpensive and easy to machine. End plates 56 provided on both sides of the rotor core in the axial direction have a function to hold down the rotor core 52 from both sides, a function to correct imbalance of the rotor core, and a function to prevent the permanent magnets 56 from coming away from the rotor core 52 in the axial direction.
A fixing member 58 includes a fastening section 62 formed in a cylindrical shape, and a pressing section 64 projecting from one end portion of the fastening section 62 in a radial direction. The fixing section 58 is fixed on the rotor shaft 54 by fastening the fastening section 62 to the rotor shaft 54 in a state where the rotor core 52 and two end plates 56 are pressed in the direction of the flange section 55 by the pressing section 64. In this way the rotor core 52 becomes fixed to the rotor shaft 54 together with the end plates 56.
The end plate 60 is formed in a disk shape having substantially the same outer shape as an axial direction end section of the rotor core 52, specifically a magnetic steel sheet constituting the rotor core 52. By forming in this way, it is possible for the end plates 60 to cause a pressing force to act on the entire surface of the magnetic steel plate at both ends of the rotor core 52 in the axial direction.
Differing from this, it is conceivable to lower cost by making the end plates of smaller diameter than the rotor core. In this case, since a pressing force in the axial direction does not act on outer peripheral sections of the magnetic steel plates positioned at both ends in the axial direction of the rotor core, as described above, it becomes an essential point to suppress how much outer peripheral sections of the magnetic steel plates open up with warping deformation towards the outside in the axial direction due to reactive magnetic force between adjacent magnetic steel plates.
For example, Japanese patent Laid-open No. 2003-304670 (patent document 1) discloses a manufacturing method of a rotor for a rotating electrical machine having a step of laminating magnetic steel sheets to form a rotor core, a step of welding a surface of a desired region of the magnetic steel sheets so as to distort the desired region and form a non-magnetic region, a step of embedding the magnets in the rotor core. As an example of forming the non-magnetic region (embodiment 2 in the patent document 1), forming a rotor core 22 and then carrying out welding by laser welding across the entire axial direction length of the rotor core 22 at a surface 30 of a region between neighboring corner sections (bridge sections) of magnetic slots 28 is described and illustrated.